Diffraction means that the laser's energy spreads as it travels through space. Doubling the distance leads to an eight-fold decrease in the number of watts per square meter. It can be reduced by using short wavelengths (more advanced technology and lower efficiency) and large mirrors (fragile and heavy). Thermal lensing is the result of a laser heating up and producing a beam much less focused than a perfect Gaussian beam. It forces the laser equipment to be reduced to cryogenic temperatures, greatly complicating the removal of waste heat (energy-consuming heat pumps must be used) and increasing the mass penalty (radiator area increases by the fourth power to a reduction in temperature).

Particle beams

A depiction of a particle beam weapon from Aviation Week, 1980

Particle beams are less sensitive to temperature changes, and have very good efficiency, but suffer from requiring huge accelerators and thermal blooming.

The two downsides to particle beams are interlinked. Thermal blooming is the expansion of hot plasma, usually at a rate of several kilometers per second. To produce a relatively focused beam at the target, relativistic effects are required to slow down the time perceived by the plasma, and reduce actual expansion rate. However, even velocities of 99.99% of the speed of light or better (and the necessary accelerator length to reach them) do not produce a beam that performs better than a small infrared laser (which has a large wavelength and a small mirror). The worst part is that a faster beam is hotter, so expands even quicker.

Railguns

Navy Railgun.

Railguns are simple to handle, and the kinetic energy at the muzzle is the energy that is delivered to the target. They are relatively compact, and do not require fragile equipment.

Railguns are limited by the ranges space combat takes place at, and the melting temperature of its components. At ranges of 10-100km, railguns can efficiently accelerate projectiles to several kilometers per second velocities and still hit targets. However, the presence of lasers can push ranges to a hundred times that, and it increases further with advancing technology. Higher velocities means that the friction between projectile and rail produces higher temperatures. Efficiency degrades as temperatures increase, creating a vicious cycle. Railguns are expected to be limited to velocities of 7-10km/s before rails and projectiles of any material melt. Even a centigee acceleration 10m wide warship these rounds can dodge at ranges of 316km.

Missiles

Missiles are very effective in space. They require no energy input, and can easily be designed to track, catch up and collide with targets at any distance.

However, missiles can be shot down. If they are forced to operate on a miniaturized version of spaceship engines, they will suffer efficiency or performance penalties. If it is a different propulsion system entirely, then the targets can outrun missiles in certain situations. Defending against missiles is massively easier than attacking with them, so defenders will always have a one-up against attackers.

So what is the solution?

Looking at all the strengths and weaknesses of those weapon systems, we reach the conclusion that these are the characteristics of a perfect weapon system for long range combat:

-Very low time to target-No loss of energy in transit-High efficiency, tolerance for high operating temperatures-Cannot be intercepted-Does not give defenders a mass advantage

Lasers, particle beams, missiles... all fail to fulfil all the criteria. One weapon system, however, is the solution.

Laser beam driven sail.

Instead of effective weaponry, this technology was initially devised as an interstellar propulsion system. Travelling between stars required a system that delivered energy to a spaceship in a way that fulfilled much of the same requirements as a weapon. Low time to target is the same as high travel velocity. No loss of energy in transit is a central focus. High efficiency leads to smaller infrastructure.

Lasers were found exceedingly inefficient as a propulsion system, achieving only 6.7N of thrust per gigawatt. This lead to ludicrous proposals such as Robert Forwards's 1984 concept that required 7.2TW lasers to operate years on end.

Particle beams were an intermediate solution, producing thrust much more efficiently, but thermal blooming meant either very little of the beam's energy reached the spaceship, or thousands of beam focusing stations had to be sent along the interstellar probe.

Particle beam propulsion concept.

Midway through this research article, published in 2000 by Geoffrey A. Landis, we obtain an interesting quote:

This would lead to a thermal beam divergence of
about 2 million kilometers per light year.
This could be reduced if the beam particles condense to larger particles after acceleration. To reduce the beam
spread by a factor of a thousand, the number of mercury atoms per condensed droplet needs to be at least a million.
This is an extremely small droplet (10^-16 grams) by macroscopic terms, and it is not unreasonable to believe that
such condensation might take place in the beam. As the droplet size increases, this propulsion concept approaches
that of momentum transfer by use of pellet streams, considered for interstellar propulsion by Singer (1980).

In that paragraph, Landis discusses the theoretical and practical lower limits for beam temperature, which decreases thermal blooming and expansion of the beam significantly. An alternative in the form of beam condensation was given. The accelerated particles merge to form small droplets, which expand much more slowly.

Singer's pellet streams are also mentioned. They were first introduced in 'Interstellar Propulsion Using a Pellet Stream for Momentum Transfer' from 1979. The idea was deemed ineffective as near-lightspeed pellets would be knocked off-course by interstellar gas, and automation was needed to bring them back into position. Such automation would have to fit onto milli0gram sized pellets, and survive hundreds of thousands of Gs during launch. It is not available even today.

But back to space warfare.

We do not need near-lightspeed projectiles, nor is there interstellar gas to knock projectiles off-course. The pellet gun is perfectly suited to our requirements. It shoots tiny metal projectiles from dozens to hundreds of kilometers per second. There are design challenges, but it:

-Can cross space combat ranges in sufficient time-Does not lose energy in transit-Extreme efficiency is possible (99.9%+)-Operates on coilgun or particle accelerator principles-Difficult to detect-Can be rapid-fired to bypass interceptors and Whipple shield defenses-Negligible ammunition massHow does it work?

Let's work out the requirements in two different situations:Plausible future combatTarget accelerates at 0.1m/s^2Combat range is 1000kmTarget profile is 100mExtreme future combatTarget accelerates at 10m/s^2Combat range is 10000kmTarget profile is 100m

In plausible future combat, the target takes a minimum of 32 seconds to move outside of their profile. A projectile fired with zero lead time must cross 1000km in this time to hit it. The projectile velocity must be 31km/s or better.

In extreme future combat, the target takes a minimum of 3.2 seconds to move outside of their profile. A projectile fired with zero lead time must have a 3100km/s velocity to catch the target.

The pellets can be small. A 200g pellet of tungsten is a sphere only 3.3cm in diameter and can be accelerated to 31km/s at the cost of 1MJ, and it will deliver 1MJ to the target.

A 3100km/s pellet of 2 micrograms can be accelerated with only 10MJ of energy, and it will deliver all the 10MJ to the target.

You can reduce the pellet's velocity, and reduce the energy required by square. The excess energy will allow you to shoot several more projectiles, covering all possible positions the target will take after firing.

To reach such velocities, an inductance coilgun paired with a temperature-resistant material is required. Tungsten and boron carbide, advanced carbon materials, allow for lower efficiencies, or alternatively, higher energies.

A 5 tesla field can eject a 15mm long, 30mm wide tungsten projectile within a length of 90 meters to 32km/s. Fed by a 100MW reactor, it can shoot 100 projectiles per second, divided between several barrels. If all projectiles hit the same surface, then they will impact with the force of 24kg of TNT, per second.

Alternatively, that same power output can fire a single projectile of 1 gram to 447km/s. It would be able to hit a target 50cm across in plausible future combat.

The extreme future combat coilgun with a 25 tesla field would also require 90 meters to deliver 10MJ of kinetic energy to a 2mm wide, 1mm long carbon nanotube cylinder.

Conclusion

The pellet gun uses reasonable amounts of energy to deliver small projectile at very high velocities. Unlike a particle beam or laser, it does not suffer any loss of energy during transit, and is very efficient.

In terms of worldbuilding, warships that use pellet guns will make space combat resemble Big Gun warfare of the first half of the 20th century. Large targets will have to accelerate quickly to dodge incoming projectiles. There is a niche for nimble, small spacecraft that can dodge projectiles at much closer ranges than lumbering battleships. Smaller, rapid fire guns will deal with these 'fighters'. Lasers play a defensive role, but missiles will be obliterated by the impact of a pellet.

Staying outside of 'combat range' won't work as it does in laser-dominant warfare, as pellets do not dissipate with distance. High energy-per-pellet 'sniper' guns can deal with spacecrafts attempting to do this.

Muzzle ports can be as small as 5cm or less. Unlike the large lens of a laser system, they allow warships to be enclosed in thick, sloped armor and fully resemble daggers in space.

66 comments:

So the ultimate weapon of space warfare is... the machine gun? That's unexpected.

By the way, if all "standard" weapon systems are not efficient at extreme range from one reason or another... how is that a problem for SF writers? Extreme ranges are boring anyway. Finding ways for space warfare to NOT devolve into a sniper match is usually the tricky part.

SF writers want interesting combat. Lasers force long ranges, because they cannot be dodged, and at long range, you're better off just piling on more and more powerful lasers.

With pellet guns, effectiveness is a flat rate, but how close you can get depends on your acceleration. They are also flexible, being able to fire more often, faster, or bigger projectiles.

In such a setting, a 'space fighter' that can continuously produce 1G, shooting at very close ranges while dodging like a gundam, and a massive battleship shaped like a needle with a single massive coilgun through its keep, are both viable designs.

It's the diversity of tactics and flexibility in the designs which should interest an SF writer.

I have mentioned this before, but it might not be so difficult to dodge lasers at range, as precision at range would be difficult to attain. Spot size is not the problem. Keeping that spot on a target of a certain size IS, especially if you need to keep that laser spot on a specific target spot long enough to burn through layers of armour.To give a general idea of the problem: at a distance of 100 000 km, a beam precision of 1 arc millisecond would yield an error of just under 1/2m. This does not even address the problem of trying to control a large lens or mirror within an arc ms of error at any speed.

What would the launcher look like? A coilgun? What would be the losses on the launcher's end?I like the idea of a pellet-propelled projectile, I wish such externally-powered drones (laser and pellet) were available in CoaDE and try it out.

How would tracking be affected by the delay between launch and arrival time of the pellets?

I disagree with your statement that you cannot dump the stored energy of small power source into a laser. On the contrary, that seems to be the way to go about it. Lasers obviously have thermal limits, but you could pump a huge amount of energy into a laser if you took the proper design steps so that it can handle these large spikes of energy. In fact it would be better to use a laser weapon in this fashion as it would allow you to apply the whole energy of the beam into a much smaller pulse, making it more effective in transferring it's energy into the target.

Sorry, I had should have explained it better. A pellet gun will accept much higher watts than a laser of similar size and mass. pulsed laser will also heat up much, much more quickly than a continuous laser, so it will have a large M^2 value and be less focused. This is the reason why real life pulsed lasers only have low pulse energies.

What will it look like? Most likely a highly developed version of "Have Sting", with the barrel of the gun being the spinal mount around which the ship is built. For a good illustration, check out http://www.aerospaceprojectsreview.com/blog/wp-content/uploads/2015/09/ussp03ad2.jpg. Scott Lowther does some amazing work, so check out the rest of his blog and site as well.

Atomic Rockets does have worked examples of coilguns (AKA Mass drivers), and there are some very definite limitations as to size and velocity. In the same section, there are discussions on massive FEL's tuned to X-ray frequencies (the fabled Ravening Beam of Death, capable of cutting through metal and ceramic at one light second), and using nuclear weapons to drive pellets, liquid metal and even tight plasma beams at speeds ranging from 100km/sec to 10% the speed of light.

I had a few questions that in part due to my lack of knowledge in hard science.

1.) Will the pellets be ionized? This question arises in part from me not knowing what material the pellets are made out of and knowing magnetic fields can ionize some materials. If they are not ionized, how viable would they be if they were ionized (I'm thinking of a system like Terminator's plasma gun)?

2.) Would a casaba howitzer (used in missile form, as described in their dedicated post on this blog) be viable in this setting?

3.)So, I guess we found the justification for a destroyer-like class of starship? I remember William over at the FWS blog say this ship class is unlikely to exist if other conventional weapons are used.

1) The coilguns will have to rely on inductance. See here: http://www.coilgun.eclipse.co.uk/coilgun_basics_3.html.

The pellets will not be limited by their Curie point, but will have instead the much more robust limit of melting temperature.

Ionizing the pellets will provide an extremely poor mass/charge ratio. They suffer from the square-cube law, meaning that the surface area they present decreases in proportion to their volume as they get bigger. When we compare it to the 1:1 mass/charge ratio of an electron, an ionized pellet is not really comparable. A plasma is a gas, not a solid. It would burst apart under the magnetic pressures of acceleration, unless you held it very still. This means you can only use small quantities... and you end up with a particle beam weapon.

2) In this setting, casaba howitzers are very expensive. On the level of modern nuclear weapons, and there's some politics behind the scenes: uranium is strictly regulated, and all warships use low grade thorium for fuel. In other settings, you can easily open up the supply of uranium and have Casaba Howitzers slash warships to pieces of thousands of kilometers away.

3) As explained in 'A Constellation of Warships', specialized spacecraft are the best way to design them. Therefore, you might have a warship entirely dedicated to mounting a huge laser, and another equipped only with defensive weapons. A 'destroyer' can pop up from the evolution of a warship designed only to destroy incoming missiles. Instead of an 'anti-submarine destroyer' today, we'll have an 'anti-missile destroyer'.

I enjoy answering these questions, and never hesitate to do the same in the future. I also reply to comments on older posts as promptly as I can.

Another excuse to have "Laser destroyers" could also be having that literally be their secondary role. Blinding the laser optics of enemy warships.

To do this they need to get into laser range, so they have to be small and maneuverable to evade enemy coilgun attacks. Once they are in range, they blind the enemy's point defense and fire control systems, leaving them vulnerable to a missile attack.

Such a vessel would also make a good escort. However I'm not convinced that there is any reason not to put secondary weapons on large warships. A set of laser optics is lighter than missiles or coilguns, and will have plenty of power available if the ship has any kind of respectable engines. Ships with only lasers I can see, but if you can mount missiles or coilguns, I don't see what you gain by leaving out a laser. It would be the equivalent of a Battleship's secondary battery, or a tank's co-axle machine gun.

Blinding optics does not destroy the laser. At certain angles, it can continue shooting. Sweep the area your beam is coming from, and you'll find yourself at close range to a battleship laser.

Second, at close range, sensors like radar are quite effective. They cannot be blinded and you won't have the power output to jam them.

The worst part is that the battleship's main weapon would be a pellet gun. Ypu'd be risking your life and spaceship to neutralize a battleship's secondary armament at best. Blind firing will get you eventually.

The problem with lasers is not the mass of the optics, but the laser generator and the heat pumps and extra radiator area. Why not mount a bigger pellet gun instead?

So you say that point defense is best handled by craft mounting smaller pellet guns and capable of more rapid rotation? Sword battleships and dagger escorts?

I'm still not convinced that ships will only have one weapon system, even if a laser requires extra hardware, it's still cheaper to mount that extra hardware than to build a whole separate ship to serve as an escort. In addition to the Lens, laser generator and thermal hardware you mentioned, the escort will need it's own power source, propulsion, avionics, and crew. Ships have mounted secondary batteries since the introduction of torpedo boats, and these have only gotten bigger since the introduction of aircraft. A modern AEGIS cruiser has some of the greatest diversity in armament in naval history. There won't be any submarines in space, but I'm not convinced the mass savings of a point defense laser system are worth it.

An ideally protected battleship will have dedicated escorts as well, but one of those will effectively be welded in place.

Battleships have coilguns lasers and armorCruisers have missiles and lasersAnd destroyers just have lasers

A laser "mauler" to take down incoming kinetic energy rounds at extreme range might be what you are thinking of, but the space environment changes a lot of things.

Protecting the laser optics will be an important part of the equation, but there are a number of ways to do this. I envision Laserstars working with optical lasers to actually look a bit like this: > /

The V is the spacecraft itself, with the wide end pointed at the enemy. The laser generator shines out of the point, to the beam spreader mirror (the /), which can redirect the beam at a target or hand it off to a drone mounted fighting mirror. If you have enough fighting mirrors, the main optics can be hidden and which mirror is going to be used can be randomized to prevent an "eyeball frying contest" (as Rocketpunk Manifesto described laser vs laser combat). If you are not keen on mirrors, turn the arrangement around but the / becomes a diffraction grating instead of a mirror, which is much more difficult to damage than a mirror.

As per our host, I would see any large spacecraft carrying secondary point defense weapons, but once again, the space environment makes it different. A "Kirklin Mine" as described in Atomic Rockets, is simply a small metal plate fired in the path of an incoming kinetic energy round, and the kinetic energy of high speed space travel is enough to destroy or severely damage the missile. This may look more like ERA "bricks" on a Russian tank than a CIWS gun mount.

A simpler solution to protecting your laser is to shoot off the beam from the side. An invisible-to-the-enemy reflector bounces the beam to one of the numerous mirror drones you deployed at the start of the battle.

Something like a blacklight glass that is transparent to only a short range of wavelengths could be another solution, before Free Electron lasers become commonplace.

Point defense would have to be of the 'independent' type, as in, it does not require the electrical components, generator, capacitor, heat pumps and radiator of of energy-dependent systems. Necessarily, these will be based on kinetics: point defense cannons, anti-missile missiles, EFP plates, reactive armor, ect.

A laser point defense system is only worthwhile if the cost is sunk in a primary laser weapon.

Specific to pellet guns, kinetic defense becomes less effective. Dumb armor wins out over AMMS and EFP plates by volume of firepower. In a classic kinetics vs kinetics scenario, the attacker takes a massive mass penalty by having to accelerate his warheads, while the opponent can just sit and catch them.

With pellet guns, the projectiles can be fired at very high rates of fire with no extra marginal cost (only the pellet and a few nanograms of uranium from the reactor) while defending uses a lot more mass per projectile intercepted. The defender/attacker mass advantage is reversed, which makes for more interesting battles.

The high rate of fire of Coilguns (I refuse to call them pelletguns) makes ERA a bad investment. You will run out of armor before they run out of bullets. The lasers I am proposing would be for shooting down missiles and unarmored spacecraft. I don't see thermodynamics being very forgiving to the laser side if you try to shoot down rapid fire solid projectiles with lasers. Space debris maybe, but if the enemy can just keep shooting more projectiles, the laser is going to overheat faster than they run out of ammo.

The 'pellet' gun is to distinguish the very-high-velocity, low-mass projectile weapons from the low velocity, high-mass projectile launchers. One is useful at laser combat ranges, the other is restricted to a few hundred.

Its unlikely lasers are able to switch between tiny pellets at all, much less track them with any kind of accuracy.

A realistic laser has a power threshold. Under that threshold (in MW), it can stay cool indefinitely. Over that threshold, it progressively heats up as the cooling system cannot catch up. This leads to thermal lensing effects and a less tightly focused beam. The end result of a laser left to overheat is a defocused beam less effective than the same beam with less MegaWatts, but better focused.

A "pellet gun" type weapon would be very difficult to deal with. The current USN thinking on attacks like the is the "shoot the archer, not the arrow", so the launching spacecraft will be subjected to either a saturation attack by missiles or kinetic energy weapons outside of the assessed range of the "pellet gun", or the RBoD is going to slowly and magnificently swing the main mirror around to fry the target at extreme range.

Assuming the enemy is known to have a "pellet gun" battery and the effects of firing can be identified (heat output fluctuations), a Casaba-Howitzer could be fired back to vaporize the pellets and hopefully damage the enemy spacecraft with a spear of high energy plasma. It would certainly mess up any sensors and external fittings as well.

Since the pellets are essentially a small scale version of the matter beam space propulsion system, it might even be possible to combine this idea with the "power web". Rather than a network of lasers and focusing mirrors or lenses, the matter bream simply sends a stream of postage stamp sized light sails on fixed trajectories which properly equipped spacecraft intercept for propulsion. After a certain time of flight, the matter beam is moving at a considerable velocity, so military spacecraft can redirect the beam using on board lasers to redirect the miniature lightsails, presenting the opponent with a cloud of fast moving particles. The effect isn't as drastic as a tungsten pellet, but serves as a cloud of chaff, causes him to redirect the laser to move the cloud out of the way to get a line of sight, and has the potential to sandblast the more delicate external fittings off a spacecraft that doesn't get out of the way.

I think the USN tactic depends on having higher ranged weapons coupled with first-strike capability. Take down the cruisers and the massive wave of Russian missiles never get launched.

The pellet gun, as it does not lose lethality with range, just loses accuracy. The ranges cited in this post are 100% hit chances: even with maximum acceleration the moment the pellet is fired, the target cannot evade. If we accept lower hit chances, the ranges increase rapidly. If we pile on prediction algorithms and some design constraints (the target cannot accelerate as well along all axis), then the range increases even more.

I think it is relatively easy to design a setting where lasers are outranged by kinetics.

The Casaba Howitzer is a special case. It is to spaceships what nuclear missiles are to armies today: a weapon that totally outclasses conventional warfare and redefines how battles are played.

With CHs, we get a filthy mix of the worst of laser and missile dominated battlefields: the ability to strike down a target as soon as you can see them, and the ability to fire your entire ammunition load in one go. Its not a nice place to be.

A power web consisting of tiny 'ultravelocity' kinetics is a novel idea. I had only read about laser webs and self-propelling miniature robots acting as kinetics, but pellets...

There'll always be new ideas. I might do some research and write on it.

What about planet based missile installations? The doctrine of shooting first won't really work if your enemy is a hardened bunker. Coilgun equipped battleships would have prestigious surface strike capabilities, but they won't help if the enemy is deep underground, especially if you aren't even sure where exactly the bunkers are.

A planet also reverses the supposed mass efficiency of most missile defenses. The planet isn't interested in changing course, and it already has all the mass it could ever need. If the attacker isn't willing to RKV the planet into a ball of molten iron, the planet will have an advantage in Intelligence (no stealth in space, but plenty of stealth underground), Logistics (the supplies are already here), and Armor.

Granted, you can argue that an interstellar civilization could throw enough ships at a planet to neutralize these advantages, but between equal powers, planet based missile silos are a serious threat, and make laser point defense a better option than "Kinetic strike before missiles can be fired"

Not to mention the missiles simply need to place themselves in an orbit and wait for invading craft to smash into them with minimal chance of manoeuvring to avoid them. Throw in a bit of kessler syndrome and a planetary civilisation would certainly be able to create a dense shell of material in orbit. Could a laser defence cope with kessler syndrome?

Its slightly off topic, but if the attacking force needs to subdue and occupy the planet, it get worse when they invade a planet with oceans. Some installations, if they are submersible, might be able to move around.

That's why I still think that planetary invasions have a use, to force those missile subs to scoot around and avoid invading attack subs (which can be few in number but still present a threat), and thus reducing the window of opportunity for a attack on orbiting warcraft.

Laser defense is probably the ONLY safe way to deal with Kessler syndrome, outside of waiting for the orbits to naturally decay. The laser ablates debris on the prograde side, creating thrust, and "sweeping" (It's literally called a laser broom) the rest into a lower orbit where it will safely burn up.

Ships in high orbit will only really be vulnerable to missile attacks from the ground. Kinetic attacks will be limited by the atmosphere, they won't be able to accelerate fast enough until they get into space. And any laser instillation on the surface large enough to penetrate the atmosphere is going to be a very juicy target for orbital kinetic attacks.

I imagine the best bet for kicking enemy ships out of high orbit, is to launch a bunch of missiles on the far side of the planet, and have them all pop over the horizon from different directions at the same time, hoping to overwhelm their defenses. Since these missiles are launched from the ground, they can be much larger than ship-born missiles, and might also be heavily armored. This would be incredibly expensive, but not any more than assembling an interplanetary warfleet.

Now, some authors suggest just leaving a bucket of dirt in a retrograde orbit where the enemy will crash into it, but I imagine any competent commander would expect such an obvious trap, and plan their approach as conservatively as possible. Anybody who expects the enemy to just let them rush into their sphere of influence and preform an aerocapture maneuver deserves to catch a hypervelocity bucket of gravel in the face.

I think in this situation, Kessler syndrome is more likely to be used by the attacker. They can clear the debris field as soon as the enemy capitulates. It's better to take out the vulnerable orbital infrastructure with kenetic strikes. First this will make it (slightly) harder to aim the missiles (a smart defender will have redundant terrestrial communications and targeting systems) and the debris are also likely to hit any missiles that get launched from the surface.

The ideal environment for a laser star is probably this kind of planetary siege. It can be as big as it wants to be, because it's only real threat will be A) being overwhelmed by terrestrial missiles, or B) Kinetic strike from another space fleet.

Not much can be done about B, other than making sure you have space superiority within your immediate light cone, but in the case of A, the solution is to just make it as big as possible. Using an entire asteroid as a heatsink means you can probably shoot down an entire planets worth of missiles without breaking a sweat, and as a last resort, threaten to de-orbit the thing as a scorched earth tactic.

Such a platform however is less useful for defense, if the defender has a laser moon, the attacker will put it on the top of the Kinetic Kill list, and nothing can be done to prevent this. While it's reasonable to expect the enemy won't destroy an inhabited planet, but a purely military instillation is fair game. Trying to have it double as a star-port will likely be seen for the ruse it is. The enemy can always call it an acceptable loss, even if they wouldn't destroy a planet.

I suppose I've ventured quite far from my laser destroyer idea though. This is a planetary siege tower. It would protect battleships from lasers, but due to the difference in size, they would be the ones escorting it.

I don't think Kessler syndrome would be a great big problem for warships. It harms economic recovery, but not any ship designed to sustain multiple megajoule impacts.

Ships in high orbit will be very vulnerable to lasers. They have no horizon to hide behind, and they have low angular velocity across the sky.

A bucket of dirt is very easily detectable, as it will reflect sunlight on one side, and radiate it on the other. It will respond strongly to radar/lidar. Very very small laser pulses can disperse it without having to completely destroy it.

I think that weaponizing the Kessler syndrome is a form of terrorism. Has very little effect on hardened military outposts, armored warships and anything outside of the lowest energy (equatorial) and highest populated orbits. In return, they wreck industrial, research and habitation space stations, pierce orbital fuel tanks and lead to a big loss of life and money for little military benefit.

Kessler Syndrome would be dirty fighting.

In my opinion, this is the worst position for a laser star. Until all underground bunkers are cleared, it is at the mercy of a planetary laser. Using microwaves delivered through thick pure quartz openings, they can pass through the entire atmosphere with little absorption. High diffraction is compensated for by extreme levels of power and gigantic arrays.

10 submarines can group together their electrical output and float a microwave laser generator just under the surface. A centimeter-grade net is laid out over the ocean's surface - cheap, lightweight, easy to manufacture and roll out. It becomes a giant reflector for microwaves.

A 'microwave sea plate' of 10km width is invisible until it fires. If each submarine provides 5 Gigawatts, the entire set up can cut through 11mm of alumiumium per second at a range of 2000km.

A hardened radio version (1m wavelength) is probably impossible to detect even while firing. It can fire from underwater. At 100km width and 100GW input, it is dangerous at 300km, denying low orbits.

The attackers and defenders might even have (surprise!) comparable technology levels. Pulling gigawatts out of spaceship reactors is even easier done on land or surrounded by water to be used as a heat sink. Mobile gigawatts, buried long wavelength reflectors and a distributed Command and Control system will make defending a planet quite easy.

My assumption was always comparable technology levels. Or else the defenders wouldn't be able to afford to launch that many missiles.

If you say that planetary lasers can be effectively hidden however, then that does change some assumptions.

I'm not sure it effects the siege dynamics in the long term however. The attacking force just moves the laser star into a higher orbit, and the planet is still effectively blockaded. Any obvious surface infrastructure is still going to be rodded into oblivion. Any launch attempt is still going to be lasered to death. The planet's only hope of breaking the siege is to wait for a liberating fleet.

Now, planetary civilizations are already adapt at surviving for long periods without orbital infrastructure. This siege could effectively last for thousands of years, until the current government dies of natural causes. In fact, an enemy in orbit would only boost national unity. I could see a feudal civilization developing, ruled by an aristocratic caste living in underground bunkers. Rather than associating up/heaven with goodness, and down/underworld with badness, the sky would be the source of evil, and the gods would live deep underground.

This could even lead to an awkward situation where the rulers refuse to be liberated when the allied fleet breaks the siege for fear of losing their control over the populace. It must be an enemy trick, there is no allied fleet, our mother earth has always stood alone against the unspeakable horrors that lurk between the stars. Wireless communications are forbidden because of evil spirits/enemy jamming.

I recall one of the commenters on Rocketpunk Manifesto thought control of the planetary Hill sphere was needed to control the space around a planet, and especially if ultra long range weapon are assumed, this makes perfect sense. You control who can get in and out of the planetary gravity well, and can move yourself in or out of the gravity well with minimal energy depending on the tactical situation.

The next strategic objective would be the various Lagrange points, providing stable points for long range surveillance and firing platforms, once again without needing to use much fuel. The invading fleet can move in, capture any strategic infrastructure and establish pickets over the lower orbits.

Finally, after extensive scanning and "plinking" enemy spacecraft and satellites, and dropping "ortillery" rounds on ground targets for a period of weeks or months, the fleet can move into orbit, with laser emitters in the High Guard position in or near Geosync orbit to provide long range overwatch, and other ships moving into various low orbits, according to the tactical situation and strategic aims of the invaders. They may well move into polar orbits to ensure maximum coverage and make firing solutions from the ground difficult. As both Atomic Rockets and Rocketpunk pointed out, any serious attempt to subdue ground targets from space really requires lots of nuclear weapons, or some sort of energetic substitute (unleashing antimatter is probably a close second, or exotica like catalyzing the planet's matter with strange quarks...).

Planetary siegecraft will be long and tedious, following meticulous protocols, much like besieging a Vauban fortress in the 1600's.

So the pellets heat via inductance, and the more total velocity they gain, the hotter they get?

I bring this up because it's at least vaguely possible to use some form of microscale or nanoscale manufacturing to embed tiny rocket motors and circuitry into these pellets. They'd be far too small for sensors, but you could send a signal (maybe by a laser beam) telling pellets the new targeting data on the target ship. Each pellet remembers the ship's original targeting data and can calculate a relative correction.

But if the pellets are so hot that they are nearly melting, that would be very difficult to do.

The more total energy they get, the more they heat up. It's a small difference, but it means that a 100km/s grain of sand can end up cooler than a 10km/s ball of iron.

The whole point of pellet guns is that they shoot so fast, opponents cannot dodge out of the way before they hit. This removes the complexity and extra cost of turning each projectile into a miniature spaceship. Also, they suffer acceleration gradients of 36000 G's per meter for the most extreme designs.

Some specialized electronics designed for the Excalibur artillery round are designed to withstand 28-40 kiloGees, so it is possible, but I do not think it is a worthwhile investment.

The pellets are made of tungsten to maintain their disk-like shape while they heat up under acceleration. The wider the projectile, the shorter the coilgun required.

I'm a little unclear why a "100km/s grain of sand can end up cooler than a 10km/s ball of iron". Wouldn't it always be proportional to the mass? (aka, a projectile twice as heavy has twice as much energy at the same velocity, since 1/2 m*V^2, ergo the sand is hotter)

We could debate quite a bit on whether or not guidance is helpful or practical, but consider this. If the target can dodge at 0.1 G over 32 seconds, the target has a dV of 3.2 m/s.

Assuming a terrible efficiency for a nanoscale solid rocket motor of 50 ISP, and 10% of the projectile is fuel, the projectile has a dV of 5.5 m/s. So a ship shooting smart projectiles has almost double the combat range. The captain of the cheapskate ship is getting pummeled while his outgoing fire is missing.

Also, if the guidance is precise enough, every single one of the pellets could slam into the same place on the armor or aim for the muzzle of the enemy weapon...

The acceleration requirements are quite low, as you mentioned, and they would allow for much less stringent heat capacity requirements. However, 32 seconds (for the slowest railguns mentioned) still only displaces the warship by 1004 meters. With a target area only 2008 meters wide, the warship can easily be saturated.

In practice, I think that volume of fire, less-than-maximum acceleration along all axis, prediction althorithms and the warships' dimensions will vastly reduce the lead time required.

On the other hand, I see your point. A 10 gram projectile of beryllium (highest heat capacity) can have 10% of its mass dedicated to very stable electric solid propellant ignited by the equivalent of a microchip. It is a disk about 4cm wide and 0.5cm thick, and can easily fit all of these components. The 1000km/s+ microsized projectiles that rely on reaching the target too quickly for displacement to matter would be a different category.

This really gets into the idea of the "range" of the pellet guns. If you are aware of the gun firing (due to a sudden spike in the enemy's radiator temperature or getting a radar return off the incoming cloud of projectiles, then you have some time to manoeuvre or deploy countermeasures (whatever they are). Obviously, the farther out you can detect this, the more time you have to do something.

I would almost suggest that any combat spacecraft would have to deploy several dumb "drone" spacecraft to interpose between you and the enemy. This would (as a minimum) stop direct line of sight attacks since they would need to chew through the drone before reaching the target spacecraft. Of course, this means you can't shoot back either (LOS).

The constellation will then be devoted to calculating and predicting positions of enemy spacecraft and threats (low temperature "stealth" busses), interposing armoured "dumb drones" in the projected path of lasers and KE weapons and attempting to plot openings in the enemy screen to shoot through, or guiding missiles through.

So does this mean space navies will need to "go big" and have enough brute force firepower to blast through "dumb drones", or "go smart" and find subtle ways to predict or create openings for their weapons effects? The ultimate "go big" ploy would be to simply move the constellation behind an asteroid or a huge bladder filled with tens of thousands of tons of water to soak up incoming fire and "plow through" anyone unfortunate enough to be in the way. The ultimate "go smart" ploy would be to disperse the constellation into swarms of smaller and smaller spacecraft (imagine a militarized "server sky", with playing card sized units capable of independent movement). The kinetic energy of even small units would make this sort of attack worthwhile with a large enough swarm.

Either scenario is far, far different from the usual space opera conventions of space warfare.

I think pellet guns can provide a rich enough diversity in combat that it will allow space warfare to have a 'history': dumb, slow pellets, faster pellets, microchip pellets and so on.

The drone craft are the equivalent of spaced armor: it will be defeated by tandem projectiles. Pellets are the ultimate 'small projectile', so they will always defeat defenses against them. They are so small that unless you want to go to party-trick levels of tactics such as intercepting one pellet by another, the attacker can shoot enough pellets to outstrip any defenses you put up.

To go it an age-of-sail aesthetic, your pellet gun can fire grapeshot, chain or solid rounds. Grapeshot fragments and tears apart a thin-plate drone. 'Chain' or tandem rounds can punch through thick-plate drones and space armor. Solid shot does the most damage.

LOS is not a big issue. Defensive plate drones need to maximize their area covered per mass, so they'll be rapidly deploying sheets of plastic. Infrared signals from the warship won't be blocked. Even if they were, the timescale between firing and impact is a matter of seconds. The warship is not really going anywhere.

You forgot one major tactical option: go fast. High, sustained, multidirection thrust can drastically reduce the engagement range. Space fighters can become just as effective as massive battleships if they jink their way into closer ranges. Closer ranges do not make them move destructive, but enable them use slower and smaller pellet guns.

A certain minimal size is imposed by technological limits on coilgun size, and then again by lasers. If lasers can take out your cubesat, then the defender can start gaining a big mass advantage. If it takes a pellet gun to damage a pellet-gun warship at typical combat ranges, then the mass advantage is negated.

A large 'go big' navy hiding behind a water bag or a big rock is essentially an immobile target. Missiles will take it down. Proper missiles, with three-stage boosters, stealth warheads, 20km/s+ of deltav and gigajoule-scale impact energies.

But at the end of the day, we've attained our objective. Interesting space combat. Easy-to-justify conventional fleets for who wants them, and room for wilder extrapolations.

Just to throw something else in the mix, another future history unfolding on another blog. Watching how the assumptions *this* blogger is making creates an entirely different fleet and so on is fascinating...https://bluemaxstudios.blogspot.ca/search/label/Conjunction

As an aside, a few back of the envelope calculations (which may be quite off, my math skills are pretty basic) seem to suggest that for a true rapid fire "pellet gun" type weapon, you may have to have multiple barrels or even banks of barrels together. Each one loads and fires individually, but the fire control unit is loading and firing barrels sequentially, allowing both time for the "action" to cycle and to let the barrels cool. The effect will be something like a pipe organ or "Stalin organ" rocket launcher (or some of these multi barrel cannon developed in the Middle Ages).

While much larger and bulkier than a single barrel weapon, it certainly has the effect you are looking for.

The Conjunction universe is quite interesting. It shares many events I included for my own future history, but I believe he needs to 'toughen up' some aspects, such as how exactly the US would fragment after a war with China, why nuclear weapons would not be involved, and why Kessler Syndrome cannot be avoided at extra cost (deltaV or laser sweepers).

On topic:

A coilgun working with a few dozen megajoule shots, at high efficiency, does not really need a lot of cooldown time. A bank of capacitors will allow a rate of fire greater than the power supply can provide, but the same gun can be used to fire multiple projectiles in quick succession.

Your 'minigun' solution might be better for point defense using dumb projectiles, where volume of fire is more important than accuracy or velocity.

Also, in settings where target accelerations are lower and travel times longer, projectiles can be shot at small velocity increments that will allow them to reach the target at the same time. This replaces any need for any 'true' firing rates.

Conjunction is a great example of world building using a single set of assumptions (just not the same ones being discussed here). You probably recognize my starting assumptions are quite different as well ;-). I find some of the work outside of the Conjunction world building exercise interesting as well, including the solar electric "Tall Ships".

I may have been misreading your earlier descriptions about the pellet gun then. My impression was sheer volume of fire distributed among hundreds to thousands of pellets would overwhelm the defences and armouring of the target, hence the visual of a large block holding a 10X10 array of coilgun barrels. This might still be a valid model for a Kineticstar, especially in a high threat environment.

And a "time on target" strike...that would make for a very impressive visual.

The Tall Ships are a bit hard to believe. There's nuclear pulse propulsion, access to 'unregulated' uranium for nuclear thermal rockets, and yet they'd use solar-electric for transporting people? Never mind. Digressions.

You are actually correct about pellet guns - volume of fire can offset a lack of predictability or projectile velocity. If you have technological limits preventing you from accelerating pellets to hundreds of kilometers per second, then you have to make your slower projectiles more effective.

With those sorts of limits (which currently exist for coilguns, such as finite switching rate and magnetic momentum in the coils), maximizing gun size and energy might not be optimal. Using several guns could be more effective, for the same set of reasons why WWII battleships did not just mount the largest caliber cannon possible.

A 7-gun hexagon of pellets shooting across space has its own flair. A &-gun, time on target strike, which is basically a tall tower of pellets raining down on the target, would be a sight to behold. Oh, and there can be multiple ships.

This is starting to look like the battleships in LOGH. Massive batteries of forward facing cannons rather than the single spinal mount and turrets more popular in other anime. Side facing guns are an afterthought and mostly used for point defense.

I wonder if a particle beam would make a reasonable defense against a stream of smart pellets. It could do a reasonable job of disrupting control systems at longer ranges and boiling the pellets themselves at closer ranges.

Actually working out whether this is a practical approach or not is left as an exercise for the reader, but I'm just happy that we can finally have the independently targeting particle beam phalanx that the colonial marines promised us all those years ago.

//Particle beams are less sensitive to temperature changes, and have very good efficiency, but suffer from requiring huge accelerators//

What about cyclotrons? Yes, they are massive (they required massive magnets to bend the beam), but the linear size could be much more compact. And, the magnet mass is a technical problem, not fundamental; i.e. "with better technology", the magnets could be made smaller and lighter.

Thanks!No, not a shotgun. The pellets are single solid projectiles. This helps them get through thicker armor than multiple particles that spread their energy over larger areas.

They are coilguns, mostly, but it does not strictly rule out railguns or other acceleration methods, such as colloid particle guns.

More specifically, it is a category of weapon that shoots tiny projectiles at extreme velocities.

Active point defense is very well served by pellet guns due to extremely low lag between shooting and hitting a target, and the immediate destruction of projectiles. Lasers have zero lag, but take time to destroy a projectile. Railguns and missiles have an easier even time intercepting targets, but the lag between shooting and hitting can be much longer.

Is it possible to use special ammunition on pellet guns? Utilizing an Gun fusion design. I made a Openoffice Calc document (finally) for this and soon for other posts and I programmed some formulas in.1g Projectile, 250km/s, 250mg DT fuel burn-up with 3,125% efficiency, Yield: 4.5 GJKE: 31,25MJ, KE in Thermal 10%, 2403846 K temperature.Its few hundred thousands kelvin short of the temperature you got with your projectile. But the Velocity is higher and thereby also the momentum/pressure, it might average out.

Yeah, in the discussion thread, I settled with @Thucydides that even small, simple projectiles equipped with a microchip and a few hundred meters per second of deltaV from micro electric solid rocket motors (http://dsspropulsion.com/wp-content/uploads/2016/02/ESP_Safe_Micro_To_Macro-Website.pdf) vastly increases their range and utility.

Gun Fusion, what I usually call for kinetic-impactor fusion bullets when used as weapons, might be possible for the larger velocity pellets. The trick to using them is using stages. I'll work it out in a future post.

Can there be a usage for Laser Driven Projectiles? Breakthrough starshot gave me the idea. a 100GW Laser array on earth shall accelerate a gram-scale nano-spacecraft to 0.2 c in minutes. Laser Array efficiency 20% and Laser sail efficiency 90% means that in 99s it should reach this velocity. A 1 gram object at 20% of c has roughly 1.8TJ (or 1.85TJ if we include relativism) So for combat applications. A 10 GW FEL with 50% efficiency should be able to accelerate any object to a energy of 100 tons tnt in 100s. A 10kg Craft at 600km/s or a 100g Craft at 6000km/s.I got the 90% efficiency quote from the Solar Sail article on Wikipedia. With Metamaterials or something else that messes with the fundamental forces. With 99.99% sails we might end up with 111 tons of tnt. 1000kg x 4.5MJ = 1 ton for convenience.

To stick with convention, the power rating I use for lasers is the beam energy, not the electrical consumption.

A 10GW laser accelerating a 1 gram projectile can certainly reach relativistic speeds. Creating a 99.9% reflective layer for a specific wavelength is doable, even if some extremely lightweight materials are going to be needed ==> 0.01% absorption of a 10GW beam means 100kW. To stay at 1000K, you'd need a surface area of 1.76m^2 (one side radiating) and an area density of 0.57g/m^2. To stay at 400K, you'd need 67.8m^2 and 0.015g/m^2...

This table-sized lightcraft massing a gram accelerates at 133.33km/s^2.

At a million km separation between attacker and target, you can reach a velocity of 16330km/s, about 5% of the speed of light.

So, taken on its own, the laser-driven projectile is quite effective.

However, a good worldbuilder considers consequences and alternatives.

This laser you're using - it delivers 10GW to a target less than a meter wide across distances of a million km or more. Wouldn't it be devastating if you just focused it on your target instead?

Your projectiles can reach some pretty extreme velocities, and carry significant kinetic energy. At the same time, they are hot, visible extremely fragile. Literal puffs of gas in their path can spin them round and 'dismount' them from the laser beam. Even the lightest cloud of glitter or thinnest whipple shield made of plastic bags can cause them break up and spread their energy to the point of uselessness.

That's a total of 70GW of waste heat. It can be handled, but the point is that it will be very massive. At my 1kW/kg benchmark for electrical components, 10kW/kg for nuclear reactors and 100kW/kg for radiators, we easily end up with a system massing 10000+20000+5000+700: 35700 tons. That's with magical turbines that produce exactly the voltage the laser needs and nothing else, and many other assumptions.

If this is a bare-bones spaceship, add another 1000 tons for engines and 100000 tons for propellant. It gets 1.3x its exhaust velocity in deltaV.

If your enemy uses that 136700 ton mass as 1367 missiles massing 100 tons each? A 100 tons in space is pretty impressive. It can likely put on more deltaV than the laser-booster ship and hunt it down. Them will likely end up being cheaper althogether than the spaceship, because they can be made of simpler components. Can the laser ship shoot down 1367 missiles? If we match costs, your enemy might be fielding thousands of missiles per laser-booster.

These are the considerations that complicate a simple analysis of laser-driven projectiles. You'll have to integrate special considerations into the design that work within an environment where laser-drive projectiles become useful.

For example, extreme ranges. At 10 million kilometers, the laser sails are delivering such incredible amounts of energy that the balance between attack and defense shifts back to the attacker - an impact can sweep away glitter clouds and create plasma waves that punch through whipple shields. After all, the sails mass only a gram and you can shoot them off all day.

Maybe the lasers are what keep spaceships well away from each other. Maybe casaba howitzers. Maybe missiles cannot effectively use stealth technology to get past laser defenses, and are picked off like flies on a wall...

The proposed 1 gram sail has a area of 16m². I know that they sail would be horrible as a weapon itself, that's why i used 100g, 1g sail and 99g "Penetrator". So if the sail is destroyed midway through the penetrator detaches itself and continues flying by itself.

The 10GW was meant as input not output, I didn't considered including momentum and acceleration for the sail, just pure kinetic energy. Though after 1s (5GJ) the Sail should already be about 316km/s, after 3s about 547km/s. If it perfectly converted the laser beams energy into Kinetic, Please correct me.

I mainly wanted a Laser driven KKV because Pellet guns are limited how much acceleration on can put into a Coilgun, Relativistic coilguns would be nearly impossible to build, But Laser driven fixes this. Their combat applications seems a bit limited for spacecraft thought. Maybe they are useful as Space snipers mounted on some moons/asteroids .

I even considered Laser sails as a boosting method for my missiles. 5 ton missile, Getting 5TJ would be accelerated to 44.7 km/s.

This laser you're using - it delivers 10GW to a target less than a meter wide across distances of a million km or more. Wouldn't it be devastating if you just focused it on your target instead? Yes, thats why i come to the idea of using Laser driven projectiles as a Alternative, Why build a Missilecoilgun ,Giant Pellet Gun or FEL for each specific task when a Laser can do all three, although not as efficient as the each one. The Laser has some advantages. Its for sake a hypothetical Warship design, Using front-mounted weapons to reduce cross section and enalbe longer barrel lenghts, using multipld Pellet guns with different calibers, 6x 100mg (Unguided), 4x 1g (Microfusion(?)/Flak), 2x 10g (Fusion/Guided) All 300km/s. And a gigantic 10GW/5GW(out) FEL Laser, You did math for a 1g spacecraft which was designed to take pictures and get information about Alpha-Centauri.

I made an Excel document for my Laser-KEVs and also Needle guns (Pellet guns).All have 3000km/s Delta-V, Crater for Steel (Also have numbers for Graphene, Boron etc.)100g, 0,6 RPM, Crater: 666m³ 5,19m deep. (0,65m for Graphene)10g, 6 RPM, Crater: 66,6m³ 2,41m deep.1g, 60 RPM, Crater: 6,67m³ 1,12m deep.The smaller model is capable of drilling through 64,8m of steel in a minute, quite impressive. So Fire Rate > Energy.But then my thought came, "wait if a pellet gun has over 95% efficiency, wouldn't be able to fire even faster?"10GW Pellet gun 95% efficiency:1g, 120 RPM, 6,33m³ 1,1m0,1g, 1200RPM, 0,05m³, 0,22m (264,65m per minute!)So Pellet guns will stay the weapon of choice when you don't want to use Uber-Lasers. Also thanks for the numbers you posted for radiation/mass, that will help me designing the Warsip,Yours sincerely.

-Using the laser sail thrust formula from 'Interstellar Trade is Possible Part II', I get 133.33 Newtons, assuming 99.9% reflectivity. Sail mass is 100 grams, so acceleration is 1333m/s^2. After 3 seconds, it is travelling at 4km/s.

-I agree, laser driven projectiles can reach incredible velocities... but their primary limitation is the laser power, and the secondary limitation is how far they can focus their laser. There's no point to laser-driving if your laser is so weak that you get lower speeds than with a pellet gun, or if your focus is too broad to keep accelerating a sail over long enough distances. There are balancing factors.

-The way I see laser-driven projectiles being used is in a setting where lasers are powerful and effective at very long ranges. Because lasers are kings on the battlefield, everyone needs to have a big laser. If they skimp on the laser, their opponents can start slicing them to pieces with their longer range. So, spaceships are forced to stay outside of laser range unless they want to have a suicidal battle. BUT, how to make the most of your laser outside of effective range? Laser-driven projectiles allow you to have basically infinite range.

-Coilguns aren't necessarily the only option for accelerating pellet guns. Search 'colloid particle accelerator'. Nanogram-sized balls of mercury can be shot out of particle beam weapons to relativistic (0.99C+) velocities.

-For large payloads, laser sails accelerate too slowly to be useful. It is more convenient to use laser-thermal, laser-ablative or laser-plasma rockets. The acceleration is massively better and compensates for propellant supply imposing a 'maximum' velocity. Another option is to have the missile be two stages.The first stage is a laser-ablative plate. It deploys an inflatable lens and a second stage. The second stage is a laser sail riding on a re-focused beam. There are more tactics in the Laser Weapon Web page.

-You're welcome for the numbers. We can discuss your setting further if you want. If you want to approach topics that you feel don't fit on this blog, contact me on my email or write to me on my Google plus page.

-Thrust: It's actually 66.7 Newtons, 13,34*5=66,7 Newtons. It is a 5GW beam not a 10 GW one. Is there anything that can be improved about this?-Colloid: oh, that's how it is officially called? I already speculated about using nano particles, which gives it the advantages of Particle weapons but not the disadvantages of them. But I am certain that they will have their own problems. Also I can't find anything when I google it.-It isn't much of an setting I am creating but more the search of the perfect Hard sci-fi weapon, a presumably impossible quest. And doing something moderately useful with my knowledge about Nuclear physics and relativity.Do you have some ideas how to drive something bigger than a penny to relativistic speeds without Lasers or particle beams?

-Thrust: I would suggest simply not using the laser's photons directly. Practically anything else generates more thrust per watt.

-The downside of colloids and other macro-particle accelerator is that the charge to mass ratio of the particles is horrendous. It requires more power and/or stronger magnetic fields and/or longer accelerators to push them to the same velocity as an electron beam. There, however, tricks you can play. You can accelerate small particles at low very temperatures, and hope that they recombine in flight. The increases the average particle mass in the beam and lower dispersion.

-Like modern warfare, a weapon is only perfect for its purpose. The purpose is defined by its environments, threats and constraints... which is always much easier to create a setting and work these out instead of creating the weapons first.

-Particle beams accelerate a target several thousands of times faster than a laser, over distances several thousands of times shorter.

-Thrust: Are there any rough formulas for Laser-ablative/plasma/thermal drives? Can I model Laser-ablative/plasma as explosive propellant expansions which accelerate the spacecraft?-Particle beam: So, can't then i just dismount/deactivate the magnetic undulator of my FEL to make it a Electron particle beam weapon? And deactivate the electron recycling?

-Thrust: They are regular rocket engines. Take the laser power, multiply by two, divide by exhaust velocity, you'll have the thrust. Natural logarithm of the mass ratio, multiply by exhaust velocity, find total deltaV. All I know about laser rockets: http://toughsf.blogspot.com/2017/03/laser-launch-into-orbit.html

-That works, but you'll have to neutralize the beam or it will spread very quickly. You'll also drop to the single-pass efficiency of the accelerator.